1. Field of the Invention
The present application relates to systems for detecting a probable collision and issuing an alert regarding the probable collision.
2. Description of Related Art
Many helicopters use a tail rotor anti-torque system. On many such helicopters, the tail rotor is positioned close enough to the ground that it presents an extremely dangerous hazard to nearby personnel while the helicopter engine is running (and the rotor is turning). Also, during low-level flight, there is a risk of a tail rotor strike with the ground, ground structures, vegetation, or personnel, due in part to the difficulty or inability of a pilot to see the tail rotor and the immediate area around the tail rotor.
Because of these known problems, various efforts have been made to reduce the risk of injury and damage caused by tail rotor strikes. However, it is also important to take steps towards reducing impacts with other portions of an aircraft, particularly those that are difficult for the pilots to see such as the empennage or tail boom of a helicopter.
The primary method currently employed for avoiding rotor strikes uses a mechanical guard to impact an obstacle and transfer the energy to a less susceptible structure point on the helicopter. This method is disadvantageous due to the fact that an actual impact will still occur and this method is limited to preventing only certain types of impacts. For example, a tail stinger will only transfer energy if the stinger is impacted first; the tail stinger provides minimal protection for an impact from the side or above. A mechanical guard also serves to deter a person from moving into the danger zone of a tail rotor. However, there is still a disadvantage to this method since a person may still come into contact with the guard before their movement into the danger zone is impeded. Also, not all angles of approach are impeded by most mechanical guards.
Another method of reducing tail rotor strikes has involved various high-visibility paint schemes designed to make a turning tail rotor more visible. Outfitting tail rotors with high-visibility paint schemes has resulted in a decrease in the number of accidents due to persons walking into an operating tail rotor; however, this method is not effective in low-light or dark conditions or for preventing the helicopter from flying into obstacles.
Still further methods, such as disclosed in U.S. Pat. No. 5,371,581 to Wangler et al. titled “Helicopter Obstacle Warning System,” involve the use of a laser-based detector mounted in a location on the helicopter suitable for detecting an obstacle near the tail rotor. However, this method disadvantageously relies on optics that are prone to degraded performance in dust or other environments where the optical lenses of the system can be obscured by particulate matter in the air. The device shown is also mounted on the underside of the aircraft, limiting its field of view and can be greatly obscured by dust or other vegetation as part of an unprepared landing site. The method also relies on a mechanical device to rotate the optics. Laser-based technology can also be attenuated or blinded by certain types of particulate (i.e. snow). Laser energy can also see higher reflectivity due to a high density of particulate, making it prone to errors, false alarms, or non-alert due to blinding.
Hence, there is a need for an improved system for detecting obstacles near the tail rotor and avoiding tail rotor strikes.